The present invention relates to weigh scales used in a checkout system in which products are weighed prior to purchase. More particularly, the invention concerns weigh scales adapted for use with security features of the checkout system.
Checkout terminals have evolved to incorporate components that automatically scan a bar coded price and product identifier and that automatically weigh an item. These checkout terminals may be attended by a cashier or may form part of a self-service checkout facility in which the customer performs the scanning and weighing steps. A typical checkout terminal of this type includes a scanning station that may be in the form of the station 10 shown in FIG. 1. This scanning station includes a vertical scanner assembly 12 with a housing 13 containing the scanning hardware and a window 14 through which the scanning process occurs. The station also includes a horizontal scanner assembly 16 with a housing 17 and window 18 similar to the vertical assembly. Both scanner assemblies 12, 16 include hardware that allows the station 10 to read an identification tag associated with each item being purchased at the station. In a typical case, the identification tag is a bar code that bears encoded information about the item, such as the SKU number and price. In a station like the one shown in FIG. 1, the two scanner assemblies allow the bar code to be read from different angles.
As shown in the view in FIG. 2, the horizontal scanner assembly includes a barcode reader 20 with its own window 21 that coincides with the window 18. A similar reader is mounted within the housing 13 for the vertical scanning assembly.
Incorporated into the scanning station 10 is a weigh plate 24 (FIG. 1) on which items to be purchased are placed to be weighed. The weight plate supports the window 18 so that the barcode reader 20 beneath can operate. The weight plate is carried by support posts 25 (FIG. 2) that project from an electronic scale 26. As is known in the art, the scale may be used to simply weigh produce or may be used to verify a scanned item by comparing the measured weight to an expected weight stored in a database.
Many retail establishments utilize security features associated with certain products. These security features are typically in the form of a tag carried by or affixed to the product. The security tag includes a resonant circuit with an integral capacitor which is effective for activating an alarm at the store exit when detected by corresponding sensing equipment. These types of security tags can be deactivated by transmitting a suitable signal from an antenna that short circuits the capacitor to disable the resonant circuit. Thus, many scanning stations also include an antenna and deactivation system, such as the system 28 and coil 29 shown in FIG. 2. As illustrated, the system and coil 28, 29 are oriented directly below the weigh plate 24 (FIG. 1).
In a typical scanning station, the weigh plate 24 is a stainless steel plate because it is easy to clean and pleasing to the eye. However, the plate may interfere with the function of the deactivation system 28 and its coil antenna 29. In one mode, the weigh plate creates a closed loop that disrupts the eddy currents of the magnetic pulse generated by the deactivation system. This phenomenon attenuates the signal range of the coil 29 so that the deactivation system may work only intermittently, if at all.
In one approach to solving this problem, the metal frame of the weigh plate is split around the window 18 and incorporating a non-metallic, or plastic, structure beneath and supporting the metal plate. However, it has been found that this approach compromises the stiffness of the weigh plate which becomes highly problematic when used with low profile, high-sensitivity weigh scale technology. This scale technology typically utilizes a four load cell planar beam configuration, as represented by the four support posts of the scanning station shown in FIG. 2. The reduced stiffness means that the weigh scale can deflect under the load of an item placed thereon, which ultimately means that the measured weight will be less than the actual weight of the product. Moreover, any deflection of the weigh plate beyond a specified range can cause side loading of the load cells, which also contributes to weighing errors.
There is a need for a weigh plate construction that does not interfere with the optimal performance of the security tag deactivation systems associated with a checkout terminal or scanning station. This need must be satisfied without compromising the performance of the weigh scale, especially for low profile, high accuracy scales such as the four load cell planar beam configurations.